1. Field of the Invention
The present invention pertains to an improved process for producing a carbonaceous pitch product having a mesophase content ranging from about 50 to 100%. which is suitable for carbon fiber manufacture. More particularly, the invention relates to a process for making mesophase containing pitch capable of producing carbon fibers having enhanced properties, by contacting a feedstock for a period of time with an oxidative gas at an elevated temperature, subjecting the oxidatively treated feedstock to a heat soak in the absence of a sparging gas for a longer period of time and thereafter subjecting heat soaked feedstock to sparging with a non-oxidative gas at an elevated temperature for a time period equal to or less than the heat soak.
2. The Prior Art
In recent years extensive patent literature has evolved concerning the conversion of carbonaceous pitch feed material into a mesophase-containing pitch which is suitable for the manufacture of carbon fibers having desirable modulus of elasticity, tensile strength, and elongation characteristics.
U.S. Pat. No. 4,209,500 (issued to Chwastiak) is directed to the production of a high mesophase content pitch that can be employed in the manufacture of carbon fibers. This patent is one of a series of patents pertaining to a process for producing mesophase pitches suitable for carbon fiber production. Each of these patents broadly involves heat treating or heat soaking the carbonaceous feed while agitating and/or passing an inert gas therethrough so as to produce a more suitable pitch product for the manufacture of carbon fibers.
As set forth in the Chwastiak patent, earlier U.S Pat. Nos. 3,976,729 and 4,017,327 issued to Lewis et al. involve agitating the carbonaceous starting material during the heat treatment. The use of an inert sparge gas during heat treatment is found in U.S. Pat. Nos. 3,974,264 and 4,026,788 issued to McHenry. Stirring or agitating the starting material while sparging with an inert gas is also disclosed in the McHenry patents.
U.S. Pat. No. 3,595,946 (Joo et al.) discloses heat treating and distilling coal tar pitch to increase its average molecular weight by polymerization. Various oxidizing. dehydrogenating and polymerization agents may be employed to expedite the process. The treated pitch is spun into filament which is oxidized and then carbonized.
U.S. Pat. No. 4,474,617 (Uemura et al.) describes treating low mesophase content pitch with oxidizing gas at a temperature of 200.degree. to 350.degree. C. to produce an improved carbon fiber.
Japanese Pat. No. 65090 (Yamada et al.) describes making a mesophase pitch for carbon fiber manufacture by heat treating feed in the presence of oxidizing gas at 350.degree. to 500.degree. C.
Koppers Co. Inc. has published Ger. Offen. DE 2,221,707 patent application, which discloses manufacture of isotropic carbon fibers wherein the starting material is first reacted with oxygen and then vacuum distilled, to remove non-oxidized lower-boiling components.
U.S. Pat. No. 4,664,774 shows a method for obtaining a coal tar pitch by oxidizing heavy oils by sparging with air, followed by stripping with an inert gas stream to remove undesirable low-boiling constituents.
U.S. Pat. No. 4,096,056 discloses producing a pitch (from petroleum), having a softening point of 135.degree. C., which would define an isotropic pitch. The highest processing temperature is below the normal sparging temperature. The patent describes an oxygen treatment in a two-step process.
U.S. Pat. No. 4,303,631 shows producing a spinnable mesophase by first heat treating and then sparging with an inert gas.
U.S. Pat. No. 4,066,737 shows reaction of distillate with oxygen to produce a pitch. The process appears to produce a non-graphitizable pitch.